The present invention relates generally to cardiac pacemakers and cardiac monitoring, and particularly to rate-responsive cardiac pacemakers and pressure monitoring.
Heart failure refers to the heart""s inability to keep up with the demands made upon it. Congestive heart failure refers to an inability of the heart to pump an adequate amount of blood to the body tissues. Because the heart is unable to pump an adequate amount of blood, blood returning to the heart becomes congested in the venous system.
In a healthy heart, the heart pumps all of the blood that returns to it, according to the Frank-Starling law. Increased venous return leads to increased end diastolic volume, which causes increased strength of contraction and increased stroke volume. In addition to intrinsic control according to the Frank-Starling law, a healthy heart is subject to extrinsic control, such as stimulation by the sympathetic nervous system to enhance contractility.
In a patient experiencing congestive heart failure, intrinsic and extrinsic control mechanisms may not function properly, and consequently the heart may fail to pump an adequate amount of blood. A condition known as cardiac decompensation is used to describe heart failure that results in a failure of adequate circulation.
Failure of the left side of the heart is generally more serious than the failure of the right side. On the left side of the heart, blood returns from the pulmonary system and is pumped to the rest of the body. When the left side of the heart fails, there are consequences to both the pulmonary system and to the rest of the body. A patient with congestive heart failure may be unable to pump enough blood forward to provide an adequate flow of blood to his kidneys, for example, causing him to retain excess water and salt. His heart may also be unable to handle the blood returning from his pulmonary system, resulting in a damming of the blood in the lungs and increasing his risk of developing pulmonary edema.
Increased blood pressure within the left side of the heart is usually attendant to failure of the left side of the heart. The increased pressure may be detected by an intra cardiac pressure sensor. The sensor may be implanted in the patient""s right ventricle and may supply pressure signals to a monitor. The monitor may use pressure signals from the right ventricle to estimate the pressures in the left side of the heart.
Some patients with congestive heart failure benefit from an implanted pacemaker. A pacemaker rhythmically generates impulses that spread throughout the heart to drive the atria and ventricles. A typical pacemaker monitors the electrical activity of the patient""s heart and provides pacing to cause the heart to beat at a desired rate, such as sixty beats per minute.
A rate-responsive pacemaker adjusts the pacing rate to the changing needs of the patient. For example, a rate-responsive pacemaker may normally pace the patient at sixty beats per minute when the patient is sleeping or a rest. When the patient increases his activity, however, the pacemaker may pace the patient""s heart more rapidly to produce a higher heart rate. Rate-responsive pacemakers may sense changes in the patient""s level of activity in various ways, such as by an accelerometer, by measuring the patient""s blood temperature, by measuring the patient""s oxygen saturation, and by measuring other biological factors.
Rate-responsive pacemakers are known in the art. In addition, techniques for monitoring intra cardiac pressures are known in the art. Examples of these techniques and/or devices may be found in the issued U.S. Patents listed in Table 1 below.
All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.
As noted above, a typical rate-responsive pacemaker monitors the electrical activity of the patient""s heart. The electrical activity reflects depolarization and repolarization of the heart, and does not reflect cardiac pressures. Furthermore, although rate-responsive pacemaking can treat cardiac decompensation, the electrical signals received by the pacemaker do not indicate whether cardiac decompensation is present or whether the patient is at risk of cardiac decompensation.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to treatment of cardiac decompensation in prior art pacemakers. In particular, it is an object of the present invention to treat cardiac decompensation by modulating a rate-responsive pacemaker with a signal based upon intra-cardiac pressures.
Accordingly, the present invention includes features that combine a rate-responsive pacemaker with a pressure sensor coupled to a pressure monitor. The pressure monitor receives the pressure signal from the sensor, and detects and/or estimates a particular pressure that is indicative of the patient""s condition. This particular pressure is then used to generate a signal that causes the rate-responsive pacemaker to adjust the pacing of the patient""s heart.
A pressure indicative of the patient""s condition is the pressure in the right ventricle that causes the pulmonary valve to open. This pressure reflects the pulmonary artery diastolic pressure. The pulmonary artery diastolic pressure in turn reflects the average left atrium pressure for a cardiac cycle, and reflects the left ventricle filling pressure in diastole. During the phase when the pulmonary valve is forced open due to right ventricular ejection, the corresponding (estimated) pulmonary artery diastolic pressure (ePAD) reflects the pulmonary capillary wedge (diastolic) pressure (PCWP), which reflects mean left atrial pressure (LAP), which reflects left ventricular end diastolic pressure (LVEDP).
Past studies on ePAD indicate that there is a very strong correlation between ePAD and PCWP. This relationship can be described as follows: ePAD reflects the PCWPxe2x89xa1mean LAPxe2x89xa1LVEDP. Note that ePADxe2x89xa0PCWP, but that the two parameters have a fixed relationship: if PCWP increases, then the ePAD increases by the same increment, and if PCWP decreases, then the ePAD decreases by the same increment. Therefore, ePAD measurements made from the right side of the heart can be used to reflect left-sided left ventricular parameters, and in particular, the LVEDP.
Another feature of the invention, therefore, is a processor that monitors the pressure continuum in the right ventricle and identifies the pressure that corresponds to the estimated pulmonary artery diastolic pressure. This pressure is accurately indicative of pressures in the left side of the heart. The invention may include techniques for identifying the pressure in the right ventricle that is indicative of left side pressures.
Once the estimated pulmonary artery diastolic pressure is identified, the pressure may be used to generate a signal that is received by a rate-responsive pacemaker. The present invention includes a rate-responsive pacemaker that may be responsive to the electrical signals from the patient""s heart and/or pressure signals from the patient""s heart.
A further feature of the invention allows the patient""s physician to customize the treatment for the patient. The patient""s physician may specify, for example, suitable pacing for particular pressures. The present invention presents techniques whereby the patient""s physician can relate the pacing of the patient""s heart to the monitored pressures. The physician can further monitor the results of the patient""s therapy.
In various embodiments, one or more of the features described above may provide a number of advantages. For example, cardiac decompensation can be diagnosed by the pressure monitor, and the cardiac decompensation can promptly be treated by a rate-responsive pacemaker. A further advantage is that the patient""s estimated pulmonary artery diastolic pressure may be continually monitored, and the patient""s pacing rate adjusted accordingly.
The above summary of the present invention is not intended to describe each embodiment or every embodiment of the present invention or each and every feature of the invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.